1. Field of the Invention
This invention relates to a microstrip antenna, in particular, to a high-directivity antenna.
2. Description of Related Art
The TW Patent No. I223909 discloses a circular polarized micro-strip antenna with capacitance feed-in includes a substrate with opposite first and second surfaces, a feed-in port, a feed-in metal electrode, a radiate metal electrode, and a ground metal electrode. The substrate is a ceramic substrate with high dielectric constant. The feed-in metal electrode is formed on the first surface of the substrate, and the feed-in metal electrode is electrically connected with the feed-in port. The radiate metal electrode is formed on the first surface of the substrate, and surrounds the feed-in metal electrode, wherein a circular area is generated between the feed-in metal electrode and the radiate metal electrode. The ground metal electrode is formed on the second surface of the substrate having a through-hole to connect the first surface and the second surface for electrically connecting the feed-in metal electrode and the feed-in port.
The U.S. Pat. No. 6,879,292 also discloses a patch antenna which includes a dielectric substrate having a through-hole for disposing a feed pin.
Next, the U.S. Pat. No. 7,030,815 discloses an antenna patch coupling a connecting element through a plated through-hole of a dielectric layer.
In general, the cost for the microwave plate with low dielectric coefficient is rather high, such as Teflon plate; whereas the cost for microwave plate with high dielectric coefficient is much lower, such as the Ro4003 plate or the ceramic plate. For the conventional microstrip antenna, the larger the dimension is, the higher directivity an antenna has when using the substrate with lower dielectric coefficient. Whereas, the smaller the dimension is, the lower directivity an antenna has when using the substrate with higher dielectric coefficient.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a high-directivity microstrip antenna having higher directivity when the antenna is designed in a fixed dimension.
It is another object of the present invention is to provide a high-directivity microstrip antenna with lower manufacturing cost.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.